Electric discharge device



M r h. 21,1944. w. J. KNQCHEL M. 2 34 5 2 ELECTRIC DISCHARGE DEVICEFiled Feb. 7, 1942 INVENTQRS W.J'. KNOC'l/fl- J- J- C'f/E BY Wm ATTORNEYPatented Mar. 21, 1944 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGEDEVICE Pennsylvania Application February 7, 1942, Serial No. 429,866

4 Claims.

This invention relates to high vacuo incandescent filament electrondischarge devices and more particularly to such devices wherein thefilament is mounted upon a support means arranged to expand and contractwith the expansion and contraction of the filament during each heatingand cooling cycle.

In such devices, the high vacuo and relatively high temperaturesnormally encountered .during operation of the device makes itexceedingly difficult to provide an expandable and contractible filamentsupport means which is freely operative over an extended time period.The essential reason for this difiiculty appears to reside in thecircumstance that the coemcient of friction between clean and dcgasifiedmetal surfaces such as are normally present in high vacuo devices ismany times that of the same metal surfaces in air. It appears thatsurface metal oxides are essential to a low coefiicient of frictionbetween two contacting metal surfaces and as surface metal oxides arenot tolerable in high vacuo electron discharge devices, it is essentialto provide in such devices wherein a sliding contact betweensubstantially clean metal surfaces is provided, some means for loweringthe coefiicient of friction between the said metal surfaces.

One of the objects of the present invention is to provide a means forlowering the coefficient of friction between two slidably engaging metalsurfaces.

Another object is to provide a substitute for surface metal oxides onslidably engaging metal surfaces in expandable and contractible filamentsupporting means in high vacuo electron discharge devices.

Still another object is to provide an improved expandable andcontractible filament mount assembly for high vacuo electrical dischargedevices of the type known in the art as a triode vacuum tube.

Other objects and advantages will be apparent as the invention is morefully hereinafter disclosed.

In accordance with these objects we have discovered that the normallyhigh coefficient of friction between slidably engaging substantiallyclean and degasified metal surfaces in high vacuo may be materiallylowered by surfacing at least one of the surfaces with a thermallystable intermetallic compound having a relatively low vapor pressure inhigh vacuo, such as the sulfide, selenide and telluride compounds of thehighly refractory metals tungsten and molybdenum, or

with the thermally stable amorphous carbide compounds of the metalstungsten, molybdenum, boron and silicon.

The sulfide and telluride compounds of tungsten and molybdenum arerecognized lubricants for use in high vacuo devices as has heretoforebeen disclosed in U. S. application Serial No. 381,673, filed March 4,1941, by P. H. Brace, issued April 28, 1942, as Patent 2,280,386, andassigned to the same assignee as the present application, and in whichpatent is described the adaptation of these compounds as a lubricant inthe lubrication of roller bearings in high vacuo.

In the present invention, the sulfide, selenide and telluride compoundsas well as the amorphous carbide compounds mentioned are employed as asurfacing material for substantially clean and degasified metal surfacessustained in sliding relation to each other in an evacuated device inreplacement of or in substitution for, the usual oxide film layernormally present thereon and removed therefrom in the cleaning anddegasifying process, during the manufacture and assembly of the device,thereby to lower the coefficient of friction therebetween.

As one specific embodiment of the present invention, but not as alimitation of the same, the adaptation of the invention in theproduction of an expandable and contractible filament support means willbe described. Reference now should be made to the drawing, wherein- Fig.1 is a side elevational view of an expandable and contractible filamentsupport means adapted for use in an electrical discharge device iofbthetype known in the art as a triode vacuum Fig. 2 is an enlarged sectionalview of the same, showing the improvement made therein by the presentinvention;

Fig. 3 is a view along plane 3-3 of Fig. 1;

Fig. 4 is a view along plane 4-4 of Fig. 1; and

Fig. 5 is an enlarged view partly in section of the improvement of thepresent invention.

In the specific embodiment illustrated in the drawing, a plurality offilament lengths f] are sustained in substantially parallel spacedrelation about the periphery of disc members 011-112. The lower saiddisc member dz consists of two sections (12' and d2 sustained insubstantially the same plane transverse to the filament axis in a fixedposition by leading-in support wires m and we passing through press 1).

The upper disc member (ii is sustained in substantial parallel spacedrelation to lower disc member 022 by tubular member t slidably mountedon support rod 1* sustained in press s with its axis in substantiallyparallel spaced relation to the filament axes and at the approximatecenter of discs di and 022. The bottom end of tubular member is providedwith an annular collar 0 resting on spring means 3 operative to urgetubular member t upwardly, thereby maintaining each of the filaments intension and in substantial parallelism irrespective of variations inlength incident to variations in filament temperature. In practice, thefilament mount shown is included as usual in an evacuated envelopesealed to the mount at the annular flange b on the press p.

The several metal parts comprising the filament and its mounting means,prior to assembly, are baked in a readily removable gas, such ashydrogen, to thoroughly deoxidize the same and to saturate the metalwith the said gas. Following sealing-in and exhaust the metal parts arethoroughly degasified by heat treatment to relatively high temperaturesunder a continuously maintained exhaust at high vacuum. This treatmentnormally results in the complete removal of all surface metal oxides onthe slidably engaging surfaces of tubular member if and support rod 'r.In the prior art, this assembly and process has both required andresulted in excessive clearance between member t and support rod 1' ofnecessity to obtain the desired sliding relation between the parts,since any contact therebetween will result in the sticking together ofthe two contacting metal surfaces thereof due to the relatively highcoefiicient of friction between the oxide-free and degasified metalsurfaces. This relatively large spacing between the contacting surfacesof tubular member t and supporting rod r is undesirable and detrimentalas it introduces transverse rocking of the filament mount and unequaltension on the filaments ff thereby throwing the filaments ff out of thedesired parallelism in which they are mounted.

We have found that by the application of relatively thin surface coatingof one of the intermetallic compounds hereinabove identified to eitherone or to both of the slidably engaging metal surfaces of tubular memberif and supporting rod 1', the two said surfaces may be brought togetherin relatively close spaced relation to overcome the defect of theassembly hereinabove pointed out without the disadvantages of the partssticking together as heretofore experienced.

As an example, supporting rod 1 which is usually comprised of tungstenor molybdenum, after having been subjected to the usual heat treatmentin hydrogen to thoroughly deoxidize the same and to saturate the metalwith hydrogen is surfaced with a relatively thin coating it of finelydivided molybdenum sulfide, in suitable manner, of which painting,spraying, dipping, and tumbling are examples.

The metal surface of rod 1*, following the hydrogen heat treatment isnormally relatively rough, due to the reduction to metal of the surfacemetal oxides on the surface thereof. It appears necessary only toprovide a sufficient thickness of the molybdenum sulfide to provide aseparating film thickness of material equivalent to a surface layer ofmetal oxide. Larger thicknesses of the material may be provided, ifdesired. In this respect, the film layer of molybdenum sulfide functionsas a separating medium and not as a lubricant as in the above identifiedpatent to P. H. Brace.

Alternatively, the film layer H] of molybdenum sulfide may be applied tothe inner tubular surface of tubular support member t, which usually iscomprised of nickel.

Also alternatively, finely divided amorphous boron carbide may besubstituted for molybdenum sulfide as film layer l!) without departurefrom the present invention, and in this substitution the difference ofthe functioning of the material it) from the material employed as alubricant in the practice of the Brave invention is effectivelydemonstrated.

Where the temperatures of vacuum heattreatment of the filament assemblyto effectively degasify the several metal parts thereof is materiallyabove about GOO-700 C. or where the temperature attained by the tubularsupport member if and rod 1' during normal operation of the deviceincorporating the same is materially above about 600 C., it ispreferable to employ the amorphous carbide of one of the refractorymetals, tungsten, molybdenum, silicon and boron as a separating film Itbetween the slidably engaging metal surfaces of member t and rod 1.These mentioned materials are not detrimentally affected by heating tosuch relatively high temperatures and are thermally stable at thesetemperatures in high vacuo. On the other hand, however, the sulfide,telluride and selenide compounds of tungsten and molybdenum arethermally dissociable in high vacuo at temperatures approximating about800-1000 C., with liberation of sulfur, tellurium and selenium vaporswhich interfere with the normal operation of the electron dischargedevice.

Where previous heat-treatment of the metal parts t and r in hydrogen isnot practiced, the surface of the metal part to be surfaced with theseparating medium of the present invention may be roughened to theextent required to provide a retaining surface for the separatingmaterial without departure from the present invention.

From the above description of the present invention and from thedescription of the specific embodiment given, it is believed apparentthat the present invention is of wide utility in the art of electrondischarge devices of the high vacuo type, and all such modifications andadaptations of the same are contemplated as may fall within the scope ofthe accompanying claims.

We claim:

1. A high vacuo electron discharge device enclosing metal parts havingslidably engaging metal surfaces, means for materially lowering thecoefficient of friction between the said slidably engaging metalsurfaces, said means comprising a relatively thin film layer of aninter-metallic compound of the group consisting of the sulfide, selenideand telluride compounds of one of the metals tungsten and molydenum andthe amorphous carbide compound of one of the metals tungsten,molybdenum, silicon and boron, the said film being disposed upon thesurface of at least one of said slidably engaging metal surfaces.

2. A filament support means including a spring urged metallic tubularmember slidably sustained on a metal rod having a diameter closelyapproximating the inside diameter of the said tubular member, means tolower the coefiicient of friction between the slidably contacting metalsurfaces, said means consisting of a. loosely adherent film layer of acompound of the group including the sulfide, selenide and telluridecompounds of the metals tungsten and molybdenum and the amorphouscarbide compounds of the metals tungsten, molybdenum, silicon and boron,the said film layer being on at least one of the said slidablycontacting metal surfaces.

3. A filament support means including a spring urged metallic tubularmember slidably sustained on a metal rod having a diameter closelyapproximating the inside diameter of the said tubular member, means tolower the coefficient of friction between the slidably contacting metalsurfaces, said means consisting of a loosely adherent film layer of acompound of molybdenum sulfide and the amorphous carbide compounds ofthe metals tungsten, molybdenum, silicon and boron, the said film layerbeing on at least one of the said slidably contacting metal surfaces.

4. A filament support means including a spring urged metallic tubularmember slidably sustained on a metal rod having a diameter closelyapproximating the inside diameter of the said tubular member, means tolower the coeflicient of friction between the slidably contacting metalsurfaces, said means consisting of a loosely adherent film layer of acompound of the group including the sulfide, selenide and telluridecompounds of the metals tungsten and molybdenum and amorphous boroncarbide, the said film layer being on at least one of the said slidablycontacting metal surfaces.

WILLIAM JOHN KNOCHEL. SIDNEY JOHN CHERRY.

